Hydraulic motors



Oct. 3, 1967 R. H. WILSON 3,344,715

HYDRAULIC MOTORS Filed July 27, 1964 5 Sheets$heet 1 lilveurm Await/Er;

Oct. 3, 1967 R. H. WILSON 3,344,715

Filed July 27, 1964 HYDRAULIC MOTORS 5 Sheets-Sheet 2 Ian/smog R. H. WILSON HYDRAULIC MOTORS Oct. 3, 1967 Filed July 27. 1964 5 Sheets-Sheet 4 Oct. 3, 1967 R. H. WILSON 3,344,715

HYDRAULIC MOTORS Filed July 27, 1964 5 Sheets-Sheet 5 Invsunfi United States. Patent 3,344,715 HYDRAULIC MOTORS Ronald Holdsworth Wilson, Horsforth, near Leeds, England, assignor to Kirkstall Forge Engineering Limited, Leeds, England Filed July 27, 1964, Ser. No. 385,295 1 Claim. (Cl. 91180) This invention relates to hydraulic motors of the radial type, i.e., the type comprising an odd number of radially disposed cylinders, a rotary valve which connects the cylinders in succession to pressure and exhaust and a central output shaft carrying a two lobe cam which is driven by the pistons in the cylinders.

The cam in existing motors of this type is normally a harmonic cam, in which case the acceleration of the pistons decreases from a maximum at top dead center to zero when the cam has rotated through 45 from the top dead center position, and deceleration of the pistons increases in similar fashion from this position to bottom dead center. With such a cam, the output shaft is subject to torque fluctuations notwithstanding the fact that the motor is supplied with a constant flow of motive liquid and it has hitherto been necessary to provide the motor with at least five cylinders in order to obtain adequate smoothing of the torque fluctuations.

The invention provides a hydraulic motor of the above type which has three cylinders only and in which the cam is so shaped that the output shaft is driven at substantially constant torque. This can be achieved when the profile of the cam is such that the pistons move at constant acceleration over the first 30 of rotation of the cam from top dead center (which corresponds to a quarter of the piston stroke), then move at constant velocity over the next 30 of rotation of the cam (which corresponds to the following half of the piston stroke) and then move at constant deceleration over the next 30 of rotation of the cam.

Two embodiments of hydraulic motor according to the invention will now be described in more detail, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a longitudinal section through the first form of motor,

FIG. 2 is a corresponding cross section,

FIG. 3 is a section on the line A-A in FIG. 1,

FIG. 4 is a section on the line BB in FIG. 1,.

FIGS. 5A and 5B are diagrams showing respectively the torque imparted to the output shaft in a motor having a cam shaped in accordance with the invention and in a motor with a conventional harmonic cam,

FIG. dis a cross section through an alternative form of motor, and

FIG. 7 is a corresponding longitudinal section.

Like reference numerals designate like parts throughout the figures.

The motor shown in FIGS. 14 has three equally spaced cylinders 10 surrounding the output shaft 11 which carries the two lobe cam 12. The piston 13 in each cylinder bears against the cam 12 through the agency of a roller 14, mounted in a rocker 15 pivoted at 27 to an arm 16 which can turn about a pivot 28. The rocker 15 carries a spigot 17 which is received in a recess in the piston. A duct 18 leads to the outer end of each cylinder and is connected alternately to a pressure inlet 19 and an exhaust outlet 20 by a pintle valve 21 which is connected to the shaft 11 by a coupling. As shown in FIG. 4, the coupling consists of a plate 29, having a pair of recesses engaged by dogs 31 on the valve 21 and another pair of recesses 32 engaged by dogs 33 on the shaft 11. This coupling permits of some degree of floating of the pintle valve 21 as it is rotated by the output Patented Oct. 3, 1967 shaft 11. The valve 21 has a pair of inlet ports 23 (FIG. 3) which periodically connect the ducts 18 to the inlet 19 and two pairs of exhaust ports 24, 25, cooperating respectively with the ducts 18 and with the outlet 20, which are connected by a central duct 26 in the valve.

The advantages of the motor according to the invention over a motor with a harmonic cam will be apparent from a comparison of FIGS. 5A and 5B which show torque plotted against crank angle, i.e., angular position of the output shaft 11. As will be seen from FIG. 5B, the torque fluctuations are substantial and can only be smoothed out to an acceptable value by providing the motor with at least five cylinders. In the case, however, of the motor according to the invention and shown in FIG. 5A, each piston moves at constant acceleration over the first 30 rotation of the cam from top dead center, as indicated by the lines X, then move at constant velocity over the next 30 rotation of the cam, as indicated by the lines Y, and then move at constant deceleration over the next 30 rotation of the cam, as indicated by the lines Z. Accordingly the output shaft is driven at constant torque.

It is possible to move any of the three cylinders 10 from the position shown in FIG. 1 to a diametrically opposite position and this makes it possible to arrange all the cylinders above the shaft 11, as shown in FIGS. 6 and 7. Motors of the type in question may be fitted to the driven wheels of a vehicle provided with a hydraulic transmission and this arrangement of the cylinders is convenient where ground clearance is required to be low, as for example in the case of locomotives or crawler tractors. Apart from the difl erent disposition of the cylinders, the motor shown in FIGS. 6 and 7 diifers only from that shown in FIGS. 1-4 in that different means are provided for guiding the rollers 14 which coact with the cam 12.

Each roller 14 is mounted on a spindle 34 carried by a frame 35 which abuts against the piston 13. The spindle 34 carries at its ends guide rollers 36 which run on guides 37 on the housing of the motor.

The motor according to the invention can be used for industrial applications, e.g., for operating lifts or lock gates and it may in some circumstances find useful application as a hydraulic pump.

What I claim as my invention and desire to secure by Letters Patent is:

A hydraulic motor comprising a plurality of radiallydisposed cylinders respectively having pistons reciprocable therein in response to fluid pressure in the cylinders, a rotary valve driven by said motor for connecting the cylinders in succession to fluid under pressure and to exhaust, a central output shaft and a cam affixed to said shaft for rotation therewith, said cam having only two relatively diametrically-opposed lobes, and follower means carried by the respective pistons for operative engagement with said lobes to rotate said cam, said motor having only three cylinders angularly spaced from each other, the lobes of said cam respectively occupying diametrically-opposed halves of the cam profile, the said profile being shaped to produce a constant acceleration and deceleration of the piston movement throughout the first and last quarters respective of the power stroke of each piston, and to maintain a constant piston velocity throughout the second and third quarters of the power stroke of each piston, when the cam is driven at a constant angular velocity, the pistons and cam being arrange relatively to each other so that the first 30 degrees of cam rotation from a rotational position in which the crest of one of said cam lobes is engaged by a said follower means corresponds to the first quarter of the power stroke of the piston, the second 30 degrees of rotation of said cam corresponds with the second and third quarters of the power stroke of the piston, and the third 30 degrees 3 r 4 of rotation of the cam corresponds to the remaining 2,198,759 4/1940 Cadet 9118() quarter of the piston power stroke, to thereby generate 2,304,903 12/1942 Eppens 91.'-180 three separate output curves corresponding to said three 2,970,578 2/1961 Kohtaki 91-180 cylinders, each of said curves having angular intersec- 3,058,451 10/1962 Brown 91180 tions between said first and second quarters of said 5 3,090,363 5/1963 Stuver 91180 power stroke and between said thirdand fourth quarters of said power stroke, whereby to provide a substantially FOREIGN PATENTS smooth summation output curve of said motor. 1 210,234 7/ 1960 Austria.

. 3,678 9/1876 Great Britain. References Cited 10 120,669 11/1918 Great Britain. UNITED STATES PATENTS 65,846 6/1950 Netherlands.

717,445 12/1902 Nestius 91180 1,730,659 10/1929 Johnson et a1. 92 72 MARTIN P. SCHWADRON, Plzmary Exammer.

1,924,423 8/ 1933 Svenson 91180 PAUL E. MASLOUSKY, Examiner. 

